Electrical connectivity is accomplished by providing a contact-type conductor pattern (electrical contact) at the edge of a circuit board such as a printed circuit board on which electrical components are mounted, and then inserting the circuit board edge containing these electrical contacts directly into an electrical connector. This type of electrical connector for use with printed circuit boards is known as an edge socket connector.
FIG. 7 shows an example of a conventional edge socket connector (hereafter referred to simply as a “socket”). (see FIGS. 9 and 10 of U.S. Pat. No. 6,466,452 B2.) The socket 500 is configured as a zero insertion force (ZIF) socket suitable for attaching a small circuit board 10 on which a semiconductor memory is mounted (memory module) to a motherboard of an information-processing device such as a personal computer.
FIG. 7A is a perspective view showing the socket 500 and the small circuit board 10 to be connected thereto. The socket 500 is provided with an insulative housing 510 having a slot 510a that accepts an edge of the small circuit board 10 on which electrical contacts have been mounted, and a plurality of contacts 520 that touch elastically and connect electrically with the electrical contacts 12 of the small circuit board 10 that has been accepted. The socket 500 is mounted onto the motherboard that is not shown by soldering the tine portions of the contacts 520 that are exposed on the underside of the insulative housing 510.
A columnar positioning protrusion 530 is integrally formed at an asymmetric position (here, the position is to the right of center as viewed from the inserted small circuit board 10) along the width (in the lengthwise direction) of the insulative housing 510. This positioning protrusion 530 engages a notch 13 at the edge of the small circuit board 10, and functions to guide the small circuit board 10 to a predetermined position on the slot 510a. By providing the positioning protrusion 530 at this asymmetric position, improper insertion of the small circuit board 10 into the slot 510a is avoided, and the acceptance position along the width of the small circuit board 10 is regulated such that each electrical contact 12 will connect to the corresponding contact 520.
Elastic support arms 540, each provided with an inward facing tab 540a formed at the tip thereof for the purpose of securely holding the small circuit board 10, are disposed in opposing positions on either side of the insulative housing 510.
FIG. 7B is a perspective view showing the state when the small circuit board 10 is inserted into the slot 510a of the socket 500 and is held securely by the support arms 540.
When electrically connecting the small circuit board 10 to the socket 500 configured as a ZIF socket, after the edge of the small circuit board 10 on which the electrical contacts are provided is inserted obliquely from above into the slot 510a of the socket 500, the other edge is pushed downward, opposing the elasticity of the contacts 520, until the small circuit board 10 is parallel with the motherboard. Then, the side edges of the small circuit board 10 are secured by the pair of support arms 540 provided on each side of the socket 500. Accordingly, without requiring any force for insertion into the slot 510a, the small circuit board 10 having one edge accepted into the insulative housing 510 is attached to the socket 500, and an electrically connected state in which each electrical contact 12 elastically touches the contact 520 can be maintained.
However, because there is variance in the width of the positioning protrusion 530 and/or the width of the notch 13 of the small circuit board 10 within the allowable tolerance range, if the positioning protrusion is a member having a simple convex shape, as in the case of the positioning protrusion 530 of the socket 500, the widths may not always match, thereby creating a gap in some cases. For this reason, requests for smaller sizes and higher densities are accompanied by a problem whereby, if the center-to-center spacing (pitch) between the plurality of contacts 520 of the socket 500 becomes small, constant alignment of the center of each electrical contact 12 of the small circuit board 10 with the center of the corresponding contact 520 of the socket 500 becomes difficult to achieve, and positional shifting occurs therebetween.
FIG. 8 shows an example of another conventional socket that has been proposed to solve this problem. (See Patent Document 1, FIG. 1.) This socket 600 has basically the same configuration as that of the above-mentioned conventional socket 500, but differs in that it was devised to enable two small circuit boards 10 to be connected to its sides. In other words, the socket 600 is provided with an insulative housing 610 having two slots 610a, each of which accepts one edge of the respective small circuit board 10 provided with electrical contacts, and a plurality of contacts 620 that elastically touch the plurality of electrical contacts 12 on each small circuit board 10, and the socket 600 mounted on a motherboard that is not shown. Elastic support arms 640, each provided with an inward facing tab 640a formed at the tip thereof for the purpose of securely holding the small circuit board 10, are disposed in opposing positions on either side of the insulative housing 610. A small circuit board 10 having one edge inserted into the slot 610a, is held securely by the tabs 640a that engage the concave portions 10b at each side surface of the small circuit board 10.
Instead of a columnar positioning protrusion, a positioning protrusion 610b (see FIG. 10) having an elastic member 630 disposed at its tip, is integrally formed at an asymmetric position along the width of each slot 610a of the insulative housing 610.
FIG. 9 shows details of the elastic member 630 disposed at the tip of the positioning protrusion 610b. (See Patent Document 1, FIG. 2.) The elastic member 630 is comprised of a base part 631 into which the positioning protrusion 610b integrally formed on each slot 610a of the insulative housing 610 is inserted, a pair of support arms 632 that elastically extend and expand outward in a “V-shape” from the base part 631, and, formed on the tip of each support arm 632, a guide part 633 having a curved surface that engages the notch 13 at the edge of the small circuit board 10. The guide parts 633 are devised to have a curved shape so as to surround the tip of the positioning protrusion 610b of the insulative housing 610, and therefore, insertion into the notch 13 of the small circuit board 10 is smooth, and the spring force of the support arms 632 opened in a V-shape elastically press-fit the guide parts 633 against the inner wall of the notch 13, thereby guiding the small circuit board 10 to the predetermined position on slot 610a. As a result, improper insertion of the small circuit board 10 into the socket 600 is avoided, and the acceptance position of the small circuit board 10 is regulated so that each electrical contact 12 will connect to the corresponding predetermined contact 620.
With the conventional socket 600, the separate elastic member 630 is disposed on the tip of the positioning protrusion 610b integrally formed on the insulative housing 610, and accordingly, the guide part 633 expands elastically to constantly press-fit against the inner wall of the notch 13 of the small circuit board 10, thereby enabling a constant matching of the width of the guide part 633 and the width of the notch 13 of the small circuit board 10. As a result, there is no shifting of the acceptance position of the small circuit board 10 due to variation in the width of notch 13 of the small circuit board 10 and the width of the positioning protrusion of the socket 600.
However, as shown in FIG. 10, the pair of support arms 632 of the elastic member 630 do not always expand with left-right symmetry centered about the positioning protrusion 610b, and therefore, in response to requests for smaller sizes and higher densities, if the pitch between the plurality of contacts of the socket 600 (pitch of the electrical contacts 12 of the small circuit board 10) is made smaller, constant alignment of the center of each electrical contact 12 of the inserted small circuit board 10 with the center of the corresponding contact 620 of the socket 600 becomes difficult to achieve. Accordingly, the difficulty in regulating the acceptance position of the small circuit board 10 such that the electrical contacts 12 are aligned reliably with the contacts 620 is a problem that continues to exist.